The United States broke off talks with Russia on Monday on implementing a ceasefire agreement in Syria and accused Moscow of not living up to its commitments under the Sept. 9 deal to halt fighting and ensure aid reached besieged communities.
The confirmation that the U.S.-Russian talks on Syria have collapsed suggests that there is little hope, if any, of a diplomatic solution emerging anytime soon to end a 5-1/2-year-old civil war that has killed hundreds of thousands of people and displaced 11 million.
"The United States is suspending its participation in bilateral channels with Russia that were established to sustain the cessation of hostilities," U.S. State Department spokesman John Kirby said in a statement.
Secretary of State John Kerry last spoke to his Russian counterpart, Sergei Lavrov, on Saturday, a senior State Department official said, after Kerry threatened last week to walk away from the talks.
In Moscow, Foreign Ministry spokeswoman Maria Zakharova told Russian news agencies the United States was trying to shift blame onto Russia, which in recent days had tried to sustain the agreement.
A U.S. intelligence official said the bombing campaign was "one of the deadliest" since the civil war erupted in 2011.